This invention relates to telecommunications networks which transmit signaling information to network elements, and more particularly, to telecommunications packet switched networks employing Signaling System 7 message transfer part protocol to transmit signaling information between a Signal Transfer Point and a telephonic switch of the network.
Telecommunications systems utilize networks of computer controlled devices, more commonly known as network elements, to facilitate signaling between the telecommunications service provider's central office and the end user. Signaling relates to the transmission of messages between network elements over a control data signaling network which is separate from the voice communication circuits. Examples of telecommunication message signaling include data to provide call set-up, common channel signaling and other control signaling between network switching elements over a signaling channel separate from the voice network. Certain communications standards or protocol are required for signaling in telecommunications networks.
Recently, the Signaling System No. 7 protocol has been mandated for out-of-band signaling communication involving telecommunication network elements and has been implemented worldwide. See Travis Russell, "Signaling System 7", ISBN 0-07-054991-5, McGraw-Hill, Inc. 1995. Signaling System No. 7 (SS7) network elements are each uniquely identified by a Message Transfer Part (MTP) Signaling Point Code (PC). Network administrators set up routes through a SS7 network so that the network elements can send Message Signal Units (MSUs) from any network element to any other network element in the network.
Two types of network elements are telephonic switches and Signal Transfer Points (STPs). Telephonic switches control the telephone and service traffic that is provided by the telecommunications operating company. A key to a telecommunication service provider's success is for their public switched telephone network (PSTN) switches to provide continuous service. It is critical that the service provider's customers have the ability to communicate through the telecommunications network via the telephonic switch associated with the particular customer. Moreover, there are federal (United States) and world International Telecommunications Union Telecommunications (ITU-T) reporting requirements for SS7 failures ("outages") above a certain threshold. The Signaling Transfer Points (STPs) act as signaling hubs for concentrating signaling links so the telephonic switches do not need to be fully interconnected, thereby reducing network costs while also acting as access points to network services and gateways to other networks.
Network elements, such as STPs and telephonic switches, are interconnected by link sets, or a group of signaling links that all terminate on the same set of Signaling Point Codes (elements associated with the point code, PC). Each signaling link is identified by three parameters, the two Point Codes (PCs) at each end of the link and a Signaling Link Selection (SLS) code. Referring now to FIG. 1, a conventional deployment of a single link set 20 interconnecting an STP 22 and the single signaling interface 24 associated with the telephonic switch 26 is shown. Each network element (STP 22 or switch 26) is identified by its signaling point code assignment. Referring to FIG. 2, an SS7 network diagram illustrating link set deployment with a switch 26 and a pair of mate STPs 22A, 22B is shown. Each STP 22A, 22B has only one link set 20A, 20B, respectively, interconnecting the single signaling interface 24 at the telephonic switch. Because STPs 22 fully interconnect telephonic switches 26, it is important to the telecommunications service provider, and invariably to its customers, that the STPs must not fail. Due to network redundancy in that STPs are generally provided in mated pairs, FIG. 2, one STP 22A can take over for its failed mate 22B.
Disadvantageously, however, the telephonic switch is dependent on its lone single signaling interface 24 for its total SS7 network communication capabilities. If a hardware or software failure exists, or a generic software update is required, it is almost certain that a signaling outage will occur at the telephonic switch. Once this happens the switch becomes isolated and telephonic communication is lost at all telephonic units associated with the switch during the isolation period. Signaling communication at a switch following SS7 protocol is dependent and thus, is limited by its lone signaling interface which unfortunately leads to potential switch isolation upon operational failures, upgrades to the system or upon field events. Therefore, there is a need in the art to prevent disruption of telecommunication signaling and to increase the signaling availability and reliability at the network telephonic switch.